This invention is related to a containment basket for holding soluble anodes within the plating bath of a continuous plating line, and in particular, it is directed to a rigid, dielectric containment basket for holding soluble anodes in a horizontal plane adjacent to the surface of a sheet metal substrate being electrolytically plated in a continuous coil plating line.
It has been recognized, for example, in the present inventor's U.S. Pat. No. 5,476,578, that plating efficiency can be increased through strategic placement of the soluble anodes with respect to the substrate surface being plated. This earlier patent teaches that in a continuous high speed electroplating line, plating productivity can be improved by increasing the deposition rate of metallic coatings from the plating solution. In order to increase plating rates, the top and bottom anodes are positioned to within about 1/8" to 5/8" from the surface of the continuous flat rolled sheet product being plated. Through such strategic anode placement, in actual reduction to practice, the inventor has increased plating rates up to about 4 times faster than prior state-of-the-art electroplating technology.
However, it has also been discovered that during such electroplating operations, where the soluble anodes are contained in conductive baskets, stray electrical cross currents are emitted from the anode baskets. Anode baskets are typically manufactured from non-corrosive conductive materials such as titanium. When a plurality of such conductive baskets are arranged in a closely, spaced apart relationship, stray electrical cross currents jump the gap between adjacent baskets and form nuclei of metallic salts on basket sidewalls. These same electrical cross currents can also jump gaps and form nuclei on the plating tank sidewalls, or any other conductive equipment and apparatus contained within the tank. The nuclei or small deposits act as "thieves", that steal more and more salts and/or metals from the plating bath and thereby rob energy from the plating operation. If such salt deposits are allowed to remain in the plating tank, they will continue to grow until their increased weight causes them to break free from the baskets or walls. The free deposits either fall onto the surface of the plated sheet product, or are pulled upward into the plated product by the hydraulic surge that is created within the plating bath from the fast high speed sheet product moving through the tank. In either case, contact with the sheet steel product surface will cause damage to the plated surface and reduce product quality. In order for plating line operators to prevent such product damage, it is necessary to schedule periodic cleaning and maintenance to remove accumulated salt and/or metallic deposits from the anode baskets as well as from any other conductive surfaces and equipment within the tank that accumulate such deposits.
Additionally, it is well known that fabric or filter bags can be used with anodes to collect small particles that fall from the anodes to prevent contamination of the plating bath, and to prevent damage to the surface of the substrate. Typically, such filter bags encircle anodes that are suspended within a batch-plating bath. Filter bags present no problems in batch plating, where the plated product hangs motionless within the tank. However, in a high speed continuous plating line, where the product travels at high speeds through the bath, sludge collection bags present an array of problems. For example, in instances where the anodes are moved into close proximity with the coating surface of the substrate, to increase plating rates as taught in the present inventor's earlier patent, the forced hydraulic action created by the fast moving substrate causes the sludge bags to festoon outward toward the plated product. This can cause the filter bag to contact the moving product and damage the product by scratching the plated surface. In a worse case scenario, where the sharp edges of the speeding sheet metal strip make contact with the filter bags, the bags are ripped open and the sludge contents are poured out into the plating tank, and onto the plated sheet metal substrate. This destroys large amounts of product and contaminates the plating bath. Such events result in plant shutdown for cleaning and maintenance.